Pneumatic tire having a rubber component containing N, N&#39;-(m-phenylene) bismaleamic acid

ABSTRACT

The present invention relates to a pneumatic tire having a rubber component comprised of (A) 100 parts by weight of at least one elastomer containing olefinic unsaturation; (B) 10 to 120 phr of a filler selected from carbon black and silica; (C) 0.1 to 10 phr of N,N′-(m-phenylene) bismaleamic acid; (D) 0.1 to 0.5 phr of zinc dibenzyl dithiocarbamate; and (E) 0.1 to 5 phr of an additional cure accelerator.

FIELD OF THE INVENTION

The present invention relates to the use of N,N′-(m-phenylene)bismaleamic acid in rubber compositions for use in a pneumatic tire.

BACKGROUND OF THE INVENTION

In the manufacture of rubber articles, crude or raw rubber is compoundedwith various ingredients among which are sulfur and accelerators ofvulcanization. The primary function of an accelerator or acceleratorsystem is to increase the rate of the vulcanization process whileallowing sufficient time to mix the accelerators into the rubber at anelevated temperature before vulcanization commences. This delay beforethe initiation of vulcanization is commonly referred to as scorch time.

The properties of a final rubber vulcanizate that are of importanceinclude tensile strength, set, hysteresis, aging properties, reversionresistance and others. Other factors relating to the vulcanization whichare of importance are the rate of cure, the cure time, the scorchbehavior, the extent of cure, and tear resistance. These physicalproperties can be altered either beneficially or detrimentally throughthe inclusion of chemicals or components that impact upon the rate andstate of vulcanization. Increasing performance requirements for tirecontinues to require improvements in the performance of tire rubbercompounds.

SUMMARY OF THE INVENTION

The present invention relates to a pneumatic tire having a rubbercomponent containing N,N′-(m-phenylene) bismaleamic acid and zincdibenzyldithiocarbamate.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a pneumatic tire having a rubber component comprisedof

(A) 100 parts by weight of at least one elastomer containing olefinicunsaturation;

(B) 10 to 120 phr of a filler selected from carbon black and silica;

(C) 0.1 to 10 phr of N,N′-(m-phenylene) bismaleamic acid;

(D) 0.1 to 0.5 phr of zinc dibenzyl dithiocarbamate; and

(E) 0.1 to 5 phr of an additional cure accelerator.

The present invention relates to a pneumatic tire having a rubbercomponent containing elastomers having olefinic unsaturation. The phrase“rubber or elastomer containing olefinic unsaturation” is intended toinclude both natural rubber and its various raw and reclaim forms aswell as various synthetic rubbers. In the description of this invention,the terms “rubber” and “elastomer” may be used interchangeably, unlessotherwise prescribed. The terms “rubber composition,” “compoundedrubber” and “rubber compound” are used interchangeably to refer torubber which has been blended or mixed with various ingredients andmaterials, and such terms are well known to those having skill in therubber mixing or rubber compounding art. Representative syntheticpolymers are the homopolymerization products of butadiene and itshomologues and derivatives, for example, methylbutadiene,dimethylbutadiene and pentadiene as well as copolymers such as thoseformed from butadiene or its homologues or derivatives with otherunsaturated monomers. Among the latter are acetylenes, for example,vinyl acetylene; olefins, for example, isobutylene, which copolymerizeswith isoprene to form butyl rubber; vinyl compounds, for example,acrylic acid, acrylonitrile (which polymerize with butadiene to formNBR), methacrylic acid and styrene, the latter compound polymerizingwith butadiene to form SBR, as well as vinyl esters and variousunsaturated aldehydes, ketones and ethers, e.g., acrolein, methylisopropenyl ketone and vinylethyl ether. Specific examples of syntheticrubbers include neoprene (polychloroprene), polybutadiene (includingcis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene),butyl rubber, styrene/isoprene/butadiene rubber, copolymers of1,3-butadiene or isoprene with monomers such as styrene, acrylonitrileand methyl methacrylate, as well as ethylene/propylene terpolymers, alsoknown as ethylene/propylene/diene monomer (EPDM), and in particular,ethylene/propylene/dicyclopentadiene terpolymers. The preferred rubberor elastomers are natural rubber, polybutadiene and SBR.

In one aspect, the rubber is preferably of at least two of diene-basedrubbers. For example, a combination of two or more rubbers is preferredsuch as cis 1,4-polyisoprene rubber (natural or synthetic, althoughnatural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 10 to about 28 percent bound styrene or, forsome applications, an E-SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

The relatively high styrene content of about 30 to about 45 for theE-SBR can be considered beneficial for a purpose of enhancing traction,or skid resistance, of the tire tread. The presence of the E-SBR itselfis considered beneficial for a purpose of enhancing processability ofthe uncured elastomer composition mixture, especially in comparison to autilization of a solution polymerization prepared SBR (S-SBR).

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene-basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

A purpose of using S-SBR is for improved tire rolling resistance as aresult of lower hysteresis when it is used in a tire tread composition.

The 3,4-polyisoprene rubber (3,4-PI) is considered beneficial for apurpose of enhancing the tire's traction when it is used in a tire treadcomposition. The 3,4-PI and use thereof is more fully described in U.S.Pat. No. 5,087,668 which is incorporated herein by reference. The Tgrefers to the glass transition temperature which can conveniently bedetermined by a differential scanning calorimeter at a heating rate of10° C. per minute.

The cis 1,4-polybutadiene rubber (BR) is considered to be beneficial fora purpose of enhancing the tire tread's wear, or treadwear. Such BR canbe prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The pneumatic tire of the present invention is of conventional designhaving

(A) a carcass reinforced with biased or radially-extending cords, twoaxially-spaced bead portions, two axially-spaced sidewall portions, oneadjacent to each bead portion and a crown portion intermediate thesidewall portions,

(B) a circumferentially extending belt structure radially outwardly ofthe carcass at the crown portion and

(C) a tread section radially outwardly of the belt structure.

The rubber component of the tire of the present invention which containsthe N,N′-(m-phenylene) bismaleamic acid may be located in the carcass,part of the belt structure and/or tread. For example, as part of thecarcass, the component may be the apex, wirecoat, ply coat, squeegeecompounds, gum strips, chafer, reinforcing sidewall inserts or exposedsidewall. As part of the tread section, the component may be the treadbase or tread cap. The compound may also be the innerliner.

The rubber composition for use in the rubber component of the tire ofthe present invention contains N,N′-(m-phenylene) bismaleamic acid. TheN,N′-(m-phenylene) bismaleamic acid used in the present invention may bepresent at various levels in the rubber compounds of the presentinvention. For example, the level of N,N′-(m-phenylene) bismaleamic acidmay range from about 0.1 to 10.0 by weight per 100 parts of rubber (alsoknown as “phr”). Preferably, the level of N,N′-(m-phenylene) bismaleamicacid ranges from about 0.5 to about 5.0 phr.

The rubber composition contains a filler selected from carbon black andsilica to contribute the desired properties of the rubber component. Thefiller may be used in conventional amounts ranging from 10 to 120 phr.For example, when used, the silica filler may be added in amountsranging from 10 to 120 phr. Preferably, the silica is present in anamount ranging from 20 to 80 phr.

The commonly employed siliceous pigments used in rubber compoundingapplications can be used as the silica in this invention, includingpyrogenic and precipitated siliceous pigments (silica) andaluminosilicates, although precipitate silicas are preferred. Thesiliceous pigments preferably employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such silicas might be characterized, for example, by having a BETsurface area, as measured using nitrogen gas, preferably in the range ofabout 40 to about 600, and more usually in a range of about 50 to about300 square meters per gram. The BET method of measuring surface area isdescribed in the Journal of the American Chemical Society, Volume 60,page 304 (1938).

The silica may also be typically characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, and more usually about 150 to about 300.

Further, the silica, as well as the aforesaid alumina andaluminosilicate may be expected to have a CTAB surface area in a rangeof about 100 to about 220. The CTAB surface area is the external surfacearea as evaluated by cetyl trimethylammonium bromide with a pH of 9. Themethod is described in ASTM D 3849 for set up and evaluation. The CTABsurface area is a well-known means for characterization of silica.

Mercury surface area/porosity is the specific surface area determined byMercury porosimetry. For such technique, mercury is penetrated into thepores of the sample after a thermal treatment to remove volatiles.Set-up conditions may be suitably described as using a 100 mg sample;removing volatiles during 2 hours at 105° C. and ambient atmosphericpressure; ambient to 2000 bars pressure measuring range. Such evaluationmay be performed according to the method described in Winslow, Shapiroin ASTM bulletin, Page 39 (1959) or according to DIN 66133. For such anevaluation, a CARLO-ERBA Porosimeter 2000 might be used.

The average mercury porosity specific surface area for the silica shouldbe in a range of about 100 to 300 m²/g.

A suitable pore-size distribution for the silica, alumina andaluminosilicate according to such mercury porosity evaluation isconsidered herein to be five percent or less of its pores have adiameter of less than about 10 nm; 60 to 90 percent of its pores have adiameter of about 10 to about 100 nm; 10 to 30 percent of its pores havea diameter of about 100 to about 1000 nm; and 5 to 20 percent of itspores have a diameter of greater than about 1000 nm.

The silica might be expected to have an average ultimate particle size,for example, in the range of 0.01 to 0.05 micron as determined by theelectron microscope, although the silica particles may be even smaller,or possibly larger, in size.

Various commercially available silicas may be considered for use in thisinvention such as, only for example herein, and without limitation,silicas commercially available from PPG Industries under the Hi-Siltrademark with designations 210, 243, etc; silicas available fromRhodia, with, for example, designations of Z1165 MP and Z165GR andsilicas available from Degussa AG with, for example, designations VN2,VN3, BV3380GR, etc, and silicas available from Huber, for example HuberSil 8745.

As can be appreciated by one skilled in the art, it may be desirable toadd to the silica containing rubber compound a sulfur containingorganosilicon compound. Examples of suitable sulfur containingorganosilicon compounds are of the formula:Z-Alk-Sn-Alk-Z  IIin which Z is selected from the group consisting of

where R¹ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;R² is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbonatoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms, and n isan integer of 2 to 8.

Specific examples of sulfur containing organosilicon compounds ofFormula II which may be used in accordance with the present inventioninclude: 3,3′-bis(triethoxysilylpropyl)disulfide,3,3′-bis(triethoxysilylpropyl)tetrasulfide,3,3′-bis(triethoxysilylpropyl)octasulfide,3,3′-bis(trimethoxysilylpropyl)tetrasulfide,2,2′-bis(triethoxysilylethyl)tetrasulfide,3,3′-bis(trimethoxysilylpropyl)trisulfide,3,3′-bis(triethoxysilylpropyl)trisulfide,3,3′-bis(tributoxysilylpropyl)disulfide,3,3′-bis(trimethoxysilylpropyl)hexasulfide,3,3′-bis(trimethoxysilylpropyl)octasulfide,3,3′-bis(trioctoxysilylpropyl)tetrasulfide,3,3′-bis(trihexoxysilylpropyl)disulfide,3,3′-bis(tri-2″-ethylhexoxysilylpropyl)trisulfide,3,3′-bis(triisooctoxysilylpropyl)tetrasulfide,3,3′-bis(tri-t-butoxysilylpropyl)disulfide, 2,2′-bis(methoxy diethoxysilyl ethyl)tetrasulfide, 2,2′-bis(tripropoxysilylethyl)pentasulfide,3,3′-bis(tricyclonexoxysilylpropyl)tetrasulfide,3,3′-bis(tricyclopentoxysilylpropyl)trisulfide,2,2′-bis(tri-2″-methylcyclohexoxysilylethyl)tetrasulfide,bis(trimethoxysilylmethyl)tetrasulfide, 3-methoxy ethoxy propoxysilyl3′-diethoxybutoxy-silylpropyltetrasulfide, 2,2′-bis(dimethylmethoxysilylethyl)disulfide, 2,2′-bis(dimethylsec.butoxysilylethyl)trisulfide, 3,3′-bis(methylbutylethoxysilylpropyl)tetrasulfide, 3,3′-bis(dit-butylmethoxysilylpropyl)tetrasulfide, 2,2′-bis(phenyl methylmethoxysilylethyl)trisulfide, 3,3′-bis(diphenylisopropoxysilylpropyl)tetrasulfide, 3,3′-bis(diphenylcyclohexoxysilylpropyl)disulfide, 3,3′-bis(dimethylethylmercaptosilylpropyl)tetrasulfide, 2,2′-bis(methyldimethoxysilylethyl)trisulfide, 2,2′-bis(methylethoxypropoxysilylethyl)tetrasulfide, 3,3′-bis(diethylmethoxysilylpropyl)tetrasulfide, 3,3′-bis(ethyl di-sec.butoxysilylpropyl)disulfide, 3,3′-bis(propyldiethoxysilylpropyl)disulfide, 3,3′-bis(butyldimethoxysilylpropyl)trisulfide, 3,3′-bis(phenyldimethoxysilylpropyl)tetrasulfide, 3-phenyl ethoxybutoxysilyl3′-trimethoxysilylpropyl tetrasulfide,4,4′-bis(trimethoxysilylbutyl)tetrasulfide,6,6′-bis(triethoxysilylhexyl)tetrasulfide, 12,12′-bis(triisopropoxysilyldodecyl)disulfide, 18,18′-bis(trimethoxysilyloctadecyl)tetrasulfide,18,18′-bis(tripropoxysilyloctadecenyl)tetrasulfide,4,4′-bis(trimethoxysilyl-buten-2-yl)tetrasulfide,4,4′-bis(trimethoxysilylcyclohexylene)tetrasulfide,5,5′-bis(dimethoxymethylsilylpentyl)trisulfide,3,3′-bis(trimethoxysilyl-2-methylpropyl)tetrasulfide,3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide.

The preferred sulfur containing organosilicon compounds of Formula IIare the 3,3′-bis(trimethoxy or triethoxy silylpropyl)sulfides. The mostpreferred compounds are 3,3′-bis(triethoxysilylpropyl)tetrasulfide and3,3′-bis(triethoxysilylpropyl)disulfide. Preferably Z is

where R² is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms beingparticularly preferred; Alk is a divalent hydrocarbon of 2 to 4 carbonatoms with 3 carbon atoms being particularly preferred; and n is aninteger of from 2 to 4.

The amount of the above sulfur containing organosilicon compound ofFormula II in a rubber composition will vary depending on the level ofsilica that is used. Generally speaking, the amount of the compound ofFormula II will range from 0 to 1.0 parts by weight per part by weightof the silica. Preferably, the amount will range from 0 to 0.4 parts byweight per part by weight of the silica.

The commonly employed and commercially available carbon blacks used inrubber compounding applications can be used in the compositions of thepresent invention. Representative examples of such carbon blacks includethose known by the following ASTM designations, N110, N121, N134, N205,N220, N231, N234, N242, N293, N299, S315, N326, N330, N332, N339, N343,N347, N351, N358, N375, N472, N539, N550, N582, N630, N642, N650, N660,N683, N754, N762, N765, N774, N787, N907, N908, N990 and N991. Whencarbon black is used, the amount may vary. Generally speaking, theamount of carbon black may vary from 10 to 120 phr. Preferably, theamount of carbon black will range from 20 to 80 phr. It is to beappreciated that a silica coupler may be used in conjunction with acarbon black (namely, pre-mixed with a carbon black prior to addition tothe rubber composition) and such carbon black is to be included in theaforesaid amount of carbon black for the rubber composition formulation.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, modified starches, pigments, fattyacid, zinc oxide, waxes, antioxidants and antiozonants and peptizingagents. As known to those skilled in the art, depending on the intendeduse of the sulfur vulcanizable and sulfur-vulcanized material (rubbers),the additives mentioned above are selected and commonly used inconventional amounts. Typical amounts of reinforcing type carbonblacks(s), for this invention, if used, are herein set forth.Representative examples of sulfur donors include elemental sulfur (freesulfur), an amine disulfide, polymeric polysulfide and sulfur olefinadducts. Preferably, the sulfur-vulcanizing agent is elemental sulfur.The sulfur-vulcanizing agent may be used in an amount ranging from 0.5to 8 phr, with a range of from 0.5 to 6 phr being preferred. Typicalamounts of tackifier or pre-reacted resins comprise about 0.5 to about10 phr, usually about 1 to about 5 phr. Typical amounts of processingaids comprise about 1 to about 50 phr. Such processing aids can include,for example, aromatic, napthenic and/or paraffinic processing oils.Typical amounts of antioxidants comprise about 1 to about 5 phr.Representative antioxidants may be, for example, monophenols, bisphenolsand thiobisphenols, polyphenols, hydroquinones derivatives, phosphites,thioesters, naphthylamines, diphenylamine derivatives,para-phenylenediamines, quinolines and others, such as, for example,those disclosed in The Vanderbilt Rubber Handbook (1978), Pages 344through 346. Typical amounts of antiozonants comprise about 1 to 5 phr.Representative examples of such antiozonants may be, for example,para-phenylenediamines such as diaryl-p-phenylenediamines,dialkyl-p-phenylenediamine and alkyl-aryl-p-phenylenediamines. Typicalamounts of fatty acids, if used, which can include stearic acid compriseabout 0.5 to about 3 phr. Typical amounts of zinc oxide comprise about 2to about 5 phr. Typical amounts of waxes comprise about 1 to about 5phr. Often microcrystalline and paraffinic waxes are used. Typicalamounts of peptizers comprise about 0.1 to about 1 phr. Typicalpeptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

In one aspect of the present invention, the sulfur-vulcanizable rubbercomposition is then sulfur-cured or vulcanized.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a additional cure accelerator may is used in addition tothe zinc dibenzyl dithiocarbamate. The additional cure accelerator(s)may be used in total amounts ranging from about 0.5 to about 4,preferably about 0.8 to about 3.0, phr. In another embodiment,combinations of a primary and a secondary accelerator might be used asthe additional cure accelerator with the secondary accelerator beingused in smaller amounts, such as from about 0.05 to about 3 phr, inorder to activate and to improve the properties of the vulcanizate.Combinations of these accelerators might be expected to produce asynergistic effect on the final properties and are somewhat better thanthose produced by use of either accelerator alone. In addition, delayedaction accelerators may be used which are not affected by normalprocessing temperatures but produce a satisfactory cure at ordinaryvulcanization temperatures. Vulcanization retarders might also be used.Suitable types of accelerators that may be used in the present inventionare amines, disulfides, guanidines, thioureas, thiazoles, thiurams,sulfenamides, xanthates. Dithiocarbamates, in addition to the zincdibenzyl dithiocarbamate, may also be used. Peroxide curatives may alsobe present. Preferably, the additional cure accelerator is a sulfenamideor thiazole. If a second additional accelerator is used, the secondaryaccelerator is preferably a guanidine, dithiocarbamate or thiuramcompound.

The rubber compositions of the present invention may contain a methylenedonor and a methylene acceptor. The term “methylene donor” is intendedto mean a compound capable of reacting with a methylene acceptor (suchas resorcinol or its equivalent containing a present hydroxyl group) andgenerate the resin in-situ. Examples of methylene donors which aresuitable for use in the present invention includehexamethylenetetramine, hexaethoxymethylmelamine,hexamethoxymethylmelamine, lauryloxymethylpyridinium chloride,ethoxymethylpyridinium chloride, trioxan hexamethoxymethylmelamine, thehydroxy groups of which may be esterified or partly esterified, andpolymers of formaldehyde such as paraformaldehyde. In addition, themethylene donors may be N-substituted oxymethylmelamines. Specificmethylene donors include hexakis-(methoxymethyl)melamine,N,N′,N″-trimethyl/N,N′,N″-trimethylolmelamine, hexamethylolmelamine,N,N′,N″-dimethylolmelamine, N-methylolmelamine, N,N′-dimethylolmelamine,N,N′,N″-tris(methoxymethyl)melamine andN,N′N″-tributyl-N,N′,N″-trimethylol-melamine. The N-methylol derivativesof melamine are prepared by known methods.

The amount of methylene donor and methylene acceptor that is present inthe rubber stock may vary. Typically, the amount of methylene donor andmethylene acceptor that each is present will range from about 0.1 phr to10.0 phr. Preferably, the amount of methylene donor and methyleneacceptor that each is present ranges from about 2.0 phr to 5.0 phr.

The weight ratio of methylene donor to the methylene acceptor may vary.Generally speaking, the weight ratio will range from about 1:10 to about10:1. Preferably, the weight ratio ranges from about 1:3 to 3:1.

When the compound of the present invention is used as a wire coat orbead coat for use in a tire, an organo-cobalt compound may be presentwhich serves as a wire adhesion promoter. When used, any of theorgano-cobalt compounds known in the art to promote the adhesion ofrubber to metal may be used. Thus, suitable organo-cobalt compoundswhich may be employed include cobalt salts of fatty acids such asstearic, palmitic, oleic, linoleic and the like; cobalt salts ofaliphatic or alicyclic carboxylic acids having from 6 to 30 carbonatoms; cobalt chloride, cobalt naphthenate; cobalt carboxylate and anorgano-cobalt-boron complex commercially available under the designationManobond C from Wyrough and Loser, Inc, Trenton, N.J.

Amounts of organo-cobalt compound which may be employed depend upon thespecific nature of the organo-cobalt compound selected, particularly theamount of cobalt metal present in the compound. Since the amount ofcobalt metal varies considerably in organo-cobalt compounds which aresuitable for use, it is most appropriate and convenient to base theamount of the organo-cobalt compound utilized on the amount of cobaltmetal desired in the finished stock composition. Accordingly, it may ingeneral be stated that the amount of organo-cobalt compound present inthe stock composition should be sufficient to provide from about 0.01percent to about 0.35 percent by weight of cobalt metal based upon totalweight of the rubber stock composition with the preferred amounts beingfrom about 0.03 percent to about 0.2 percent by weight of cobalt metalbased on total weight of skim stock composition.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example theingredients are typically mixed in at least two stages, namely at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur-vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The rubber, silica, compound of Formula IIand carbon black, if used, are mixed in one or more non-productive mixstages. The terms “non-productive” and “productive” mix stages are wellknown to those having skill in the rubber mixing art. TheN,N′-(m-phenylene) bismaleamic acid may be added at any stage of mixingbut is preferably added in a nonproductive stage. The rubber compositioncontaining the rubber and generally at least part of the silica should,as well as the sulfur-containing organosilicon compound of Formula II,if used, be subjected to a thermomechanical mixing step. Thethermomechanical-mixing step generally comprises a mechanical working ina mixer or extruder for a period of time suitable in order to produce arubber temperature between 140° C. and 190° C. The appropriate durationof the thermomechanical working varies as a function of the operatingconditions and the volume and nature of the components. For example, thethermomechanical working may be from 1 to 20 minutes.

The above tread rubber composition is used to prepare an assembly of atire with a tread comprised of the said rubber composition. Such tire isthen vulcanized.

Accordingly, the invention contemplates a vulcanized tire prepared withthe N,N′-(m-phenylene) bismaleamic acid described herein.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. Preferably, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air or in a salt bath.

The pneumatic tire of the present invention may be a passenger tire,aircraft tire, agricultural, earthmover, off-the-road, truck tire andthe like. Preferably, the tire is a passenger or truck tire. The tiremay also be a radial or bias, with a radial tire being preferred.

The invention is further illustrated by the following example.

EXAMPLE 1

In this example, the effect of adding N,N′-(m-phenylene) bismaleamicacid and zinc dibenzyl dithiodicarbamate in a rubber compound withsilica and carbon black is illustrated. Table 1 below shows the basicrubber compound that was used in this example. Table 2 shows the amountsof zinc dibenzyl dithiodicarbamate or zinc dimethyl dithiodicarbamateused in each of Samples 1 through 4. Inventive Sample 4 contained 0.3phr of zinc dibenzyl dithiocarbamate, which is approximately equal on amolar basis to the 0.15 phr of zinc dimethyl dithiocarbamate used incontrol Sample 2. The rubber compounds were prepared in a three-stageBanbury mix. All parts and percentages are by weight unless otherwisenoted. The cure data as well as other physical data for each sample arelisted in Tables 3 and 4.

Cure properties were determined using a Monsanto moving disc rheometer(MDR) which was operated at a temperature of 150° C., 160° C. and 182°C. with a frequency of 1.67 hertz and a 0.5 degree arc. A description ofmoving disc rheometers and the use of this cure meter and standardizedvalues read from the curve are specified in ASTM D-5289. A typical curecurve obtained with a moving disc rheometer is shown on Page 794 of ASTMD-5289.

Viscoelastic properties Tan Delta and G′ were measured at 10 percentstrain using an Alpha Technologies Rubber Process Analyzer (RPA). Adescription of the RPA 2000, its capability, sample preparation, testsand subtests can be found in these references. H A Pawlowski and J SDick, Rubber World, June 1992; J S Dick and H A Pawlowski, Rubber World,January 1997; and J S Dick and J A Pawlowski, Rubber & Plastics News,Apr. 26 and May 10, 1993. TABLE 1 Rubber Compound Formulation FirstNon-Productive Mix Stage Polybutadiene ¹ 10 Natural Rubber 90 Silica 12Carbon Black 23 N,N′-(m-phenylene) bismaleamic acid 3 Wax ² 1.5 StearicAcid 2 Antidegradant ³ 1 Zinc Oxide 3 Second Non-Productive Mix StageSilica 11 Productive Mix Stage Antidegradant ⁴ 1 Zinc DimethylDithiocarbamate variable as per TABLE 2 Zinc Dibenzyl Dithiocarbamatevariable as per TABLE 2 Accelerator ⁵ 1 Sulfur ⁶ 2.4¹ Budene 1207 from The Goodyear Tire & Rubber Company² microcrystalline and paraffinic types³ paraphenylene diamine type⁴ paraphenylene diamine type⁵ sulfenamide type⁶ total of oiled (20percent) and non-oiled sulfur, expressed as sulfur

TABLE 2 Zinc Dithiocarbamate Addition Sample No. Control Control ControlInvention 1 2 3 4 Zinc Dimethyl Dithiocarbamate 0 0.15 0.3 0 ZincDibenzyl Dithiocarbamate 0 0 0 0.3

TABLE 3 MDR Sample No. Control Control Control Invention 1 2 3 4 150° C.S′ Max − S′ Min dNm 9.86 12.19 13.43 13.15 TC 90 Minutes 15.73 8.13 5.566.75 S′ Max dNm 12.54 14.89 16.14 15.7 S′ at 60 Min dNm 11.66 13.6315.43 15.24 Percent loss S′ Max at 60 Min 7 8.5 4.4 2.9 160° C. S′ Max −S′ Min dNm 10.31 12.23 13.44 13.06 TC 90 Minutes 8.16 4.53 3.18 3.76 S′Max dNm 12.94 14.92 16.04 15.7 S′ at 60 Min dNm 10.92 12.72 14.36 14.82Percent loss S′ Max at 60 Min 15.6 14.7 10.5 5.6 182° C. S′ Max − S′ MindNm 10.68 12.13 12.85 12.89 TC 90 Minutes 1.87 1.34 1.05 1.16 S′ Max dNm13.16 14.73 15.52 15.42 S′ at 60 Min dNm 9.85 10.93 11.84 13 Percentloss S′ Max at 60 Min 25.2 25.8 23.7 15.7

TABLE 4 RPA 2000 Sample No. Control Control Control Invention 1 2 3 4Samples Cure 150° C., 30 min, 1.67 Hz and 3.5% Strain Strain Sweep at100° C. and 1 Hz G′ at 1% (MPa) 1.5035 1.631 1.7745 1.7957 G′ at 10%(MPa) 1.1262 1.2287 1.3476 1.353 Tan delta at 1% 0.049 0.046 0.042 0.041Tan delta at 10% 0.077 0.067 0.062 0.064 Samples Cure 160° C., 16.4 min,1.67 Hz and 3.5% Strain Strain Sweep at 100° C. and 1 Hz G′ at 1% (MPa)1.5195 1.6789 1.8489 1.7745 G′ at 10% (MPa) 1.1124 1.2239 1.353 1.2938Tan delta at 1% 0.056 0.047 0.04 0.036 Tan delta at 10% 0.084 0.0760.071 0.07 Samples Cure 182° C. 30 min, 1.67 Hz and 3.5% Strain StrainSweep at 100° C., and 1 Hz G′ at 1% (MPa) 1.6682 1.7532 1.8489 1.8436 G′at 10% (MPa) 1.1689 1.2351 1.3311 1.3215 Tan delta at 1% 0.067 0.0610.049 0.043 Tan delta at 10% 0.096 0.089 0.077 0.075

As seen in the data of Tables 3 and 4, the combination ofN,N′-(m-phenylene) bis maleamic acid combined with zinc dibenzyldithiocarbamate shows advantages in rubber compounds as compared withthe control compound containing N,N′-(m-phenylene)bismaleamic acid aloneor combined with zinc dimethyl dithiocarbamate. Advantages includesubstantially improved reversion resistance, increase in curedstiffness, and lower hysteresis as compared with controls containingzinc dimethyl dithiocarbamate or no substituted zinc dithiocarbamate.

With reference to Table 3, Sample 4 with zinc dibenzyl dithiocarbamateshowed unexpectedly lower reversion as compared with the control samples1 through 3. Reversion was measured as the percent difference in torqueS′ at 60 minutes cure time compared with the maximum torque S′ Max, andexpressed as percent loss S′ Max at 60 min. For each of the curetemperatures considered, the reversion for Sample 4 was substantiallyless than for the controls. Surprisingly, the reversion for Sample 4 waslower even than that for the control sample 3, which had about doublethe amount of zinc dimethyl dithiocarbamate on a molar basis as comparedto the zinc dibenzyl dithiocarbamate in Sample 4. Reversion resistanceis desirable to prevent loss of properties during high temperature useof the tire.

With reference to Table 4, Sample 4 showed improved stiffness (G′) andtan delta as compared with the control samples 1 and 2, andsubstantially similar stiffness and tan delta to control sample 3. It isdesirable to have the ability to increase stiffness with reducing tandelta in tread compounds for improved handling and better fueleconomy/durability.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

1. A pneumatic tire having a rubber component comprised of (A) 100 partsby weight of at least one elastomer containing olefinic unsaturation;(B) 10 to 120 phr of a filler selected from carbon black and silica; (C)0.1 to 10 phr of N,N′-(m-phenylene) bismaleamic acid; (D) 0.1 to 0.5 phrof zinc dibenzyl dithiocarbamate; and (E) 0.1 to 5 phr of an additionalcure accelerator.
 2. The pneumatic tire of claim 1 wherein theadditional cure accelerator is selected from sulfenamides and thiazoles.3. The pneumatic tire of claim 1 wherein said elastomer containingolefinic insaturation is selected from the group consisting of naturalrubber, neoprene, polyisoprene, butyl rubber, polybutadiene,styrene-butadiene copolymer, styrene/isoprene/butadiene rubber, methylmethacrylate-butadiene copolymer, isoprene-styrene copolymer, methylmethacrylate-isoprene copolymer, acrylonitrile-isoprene copolymer,acrylonitrile-butadiene copolymer, EPDM and mixtures thereof.
 4. Thepneumatic tire of claim 1 wherein said N,N′-(m-phenylene) bismaleamicacid is present in an amount ranging from 0.5 to 5 phr.
 5. The pneumatictire of claim 1 wherein said silica is precipitated silica.
 6. Thepneumatic tire of claim 1 wherein a sulfur containing organosiliconcompound is present in said tread and is of the formula:Z-Alk-Sn-Alk-Z in which Z is selected from the group consisting of

where R¹ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;R² is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbonatoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms, and n isan integer of 2 to
 8. 7. The pneumatic tire of claim 1 wherein saidsilica is present in an amount ranging from 20 to 80 phr.
 8. Thepneumatic tire of claim 1 wherein said carbon black is present in anamount ranging from 20 to 80 phr.
 9. The pneumatic tire of claim 1wherein said tire has (A) a carcass reinforced with radially-extendingcords, (B) a circumferentially-extending sidewall portion, and (C) atread section.
 10. The pneumatic tire of claim 1 wherein said rubbercomponent is part of the carcass.
 11. The pneumatic tire of claim 1wherein said rubber component is selected from the group consisting ofthe apex, wirecoat, ply coat, squeegee compounds, gum strips, chafer,reinforcing sidewall inserts and exposed sidewall.
 12. The pneumatictire of claim 1 wherein said rubber component is part of the treadsection.
 13. The pneumatic tire of claim 1 wherein said rubber componentis the tread cap.
 14. The pneumatic tire of claim 1 wherein said rubbercomponent is the tread base.
 15. The pneumatic tire of claim 1 whereinsaid rubber component is an innerliner.